Sonicating sperm: The future of male contraception

UNC researchers find that modern ultrasound equipment normally used for physical therapy effectively reduced sperm counts in laboratory rats to levels far below what is normally seen in fertile men.

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The testis is composed of many tubes called “seminiferous tubules.” The seminiferous tubule on the left is from a testis that was not treated with ultrasound while the tubule on the right is from a testis that was treated with ultrasound.

CHAPEL HILL, N.C. -- The ideal male contraceptive would be inexpensive, reliable and reversible. It would need to be long acting but have few side effects.

New research from the University of North Carolina at Chapel Hill School of Medicine, published in BioMed Central's open-access journal Reproductive Biology and Endocrinology, used commercially available therapeutic ultrasound equipment to reduce sperm counts of male rats to levels which would result in infertility in humans.

Ultrasound's potential as a male contraceptive was first reported nearly 40 years ago. However, the equipment used at that time is now outdated and no longer available. UNC researchers used these experiments as a starting point to see if modern ultrasound equipment usually used for physical therapy could be used as a male contraceptive.

The team, led by James Tsuruta, PhD, found that by rotating high frequency (3MHz) ultrasound around the testes they were able to cause uniform depletion of germ cells through the testes.

"Unlike humans, rats remain fertile even with extremely low sperm counts. However, our non-invasive ultrasound treatment reduced sperm reserves in rats far below levels normally seen in fertile men. However, further studies are required to determine how long the contraceptive effect lasts and if it is safe to use multiple times," Tsuruta said.

The best results were seen using two sessions consisting of 15 minutes ultrasound, two days apart. Saline was used to provide conduction between the ultrasound transducer and skin, and the testes were warmed to 37 degrees centigrade. Together this reduced sperm to a Sperm Count Index of zero (3 million motile sperm per cauda epididymis).

The World Health Organization has defined oligospermia (low sperm concentration) as less than 15 million sperm per milliliter. Ninety-five percent of fertile men have more than 39 million sperm in their ejaculate.